Topologically novel copper molybdate phases based on 3,4′-dipyridylketone: Hydrothermal synthesis, structural characterization, and magnetic properties

Hydrothermal treatment of CuCl₂·2H₂O, MoO₃, and 3,4′-dipyridylketone (3,4′-dpk) in 1:1:2 mole ratio afforded the new mixed metal oxide phases [Cu₂(MoO₄)₂(3,4′-dpk)(H₂O)] (1) or [Cu₄(3,4′-dpk)₄(Mo₈O₂₆)] (2), depending on the pH of the initial reaction mixture. Compound 1 possesses unique one-dimensional (1-D) [Cu₂(MoO₄)₂(H₂O)]_n ribbons constructed from the linkage of {Cu^II₄O₆} tetrameric units through isolated [MoO₄]^2- tetrahedra. These ribbons in turn are connected into a two-dimensional (2-D) coordination polymer structure by tethering 3,4′-dpk ligands. Compound 2, containing monovalent copper ions, manifests an unprecedented “X-rail” 1-D extended structure with (6²8)₄(6⁶) topology formed from the bracketing of discrete [β-Mo₈O₂₆]^4- anions by four chains. The variable temperature magnetic susceptibility behavior of 1 was fit to a linear tetramer model, with g=2.03(3), J₁=25.8(7) cm^-1 and J₂=−46(1) cm^-1. Antiferromagnetic inter-tetramer interactions (zJ′=−0.21(3) cm^-1) were also evident. Crystallographic data: 1 monoclinic, P2₁/c, a=10.3911(11) Å, b=6.9502(6) Å, c=22.958(2) Å, β=100.658(7)°, V=1629.5(3) Å³, R₁=0.1256, and wR₂=0.2038; 2 triclinic, a=10.9000(3) Å, b=11.7912(4) Å, c=13.5584(4) Å, α=102.482(2)°, β=102.482(2)°, γ=117.481(2)°, V=1450.98(8) Å³, R₁=0.0428, and wR₂=0.0630.